<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <form>
    name:
    <input type="text" name="FirstName" value="zhangsan" size="20">
    <span style="display: none;">请输入你的电话号码</span>
    <br />
    <input type="submit" value="Submit">
  </form>
  <script src="https://cdn.bootcdn.net/ajax/libs/jquery/1.12.4/jquery.js"></script>
  <script>
    $(function () {
      // submit
      $('form').submit(function () {
        alert('Submitted')
      })

      // focus
      $('input').focus(function () {
        // fadeOut是动画 我们后面会讲到
        $('span').css('display', 'inline').fadeOut(2000);
      });

      // 其他的事件大家自己试一下
    })
    
  </script>
</body>
</html>